Metronidazole, marketed under the brand name Flagyl.


It is an antibiotic and antiprotozoal medication.



Of  nitroimidazole class. 



It inhibits nucleic acid production  by disrupting the DNA of microbial cells.



Its function occurs when it is partially reduced,  only occurring in anaerobic bacteria and protozoans, therefore has relatively little effect upon human cells or aerobic bacteria.



It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vaginosis.



Effective for:dracunculiasis, giardiasis, trichomoniasis, and amebiasis, for a first episode of mild-to-moderate Clostridium difficile colitis if vancomycin or fidaxomicin is unavailable.



Is available by mouth, as a cream, and by injection into a vein.



Pregnancy category US: B (No risk in non-human studies).



Routes of administration: mouth, topical, rectal, IV, and vaginal.



Bioavailability- 80% by mouth), 60–80%  rectally, 20–25%vaginally.



Protein binding 20%.



Metabolism Hepatic



Elimination half-life 8 hours.



Excretion Urine (77%), faeces (14%



Side effects:  nausea, a metallic taste, loss of appetite, and headaches.



Occasionally seizures or allergies to the medication may manifest.


Adverse effects include: peripheral neuropathy, nausea, and with concurrent alcohol use a disulfiram like reaction with nausea and a metallic taste.



Sources disagree over safety in pregnancy and breastfeeding.


Not recommended for women who are pregnant to a breast-feeding and should not be using the elderly or  in patients  with comorbidities



Primarily uses: bacterial vaginosis, pelvic inflammatory disease, pseudomembranous colitis, aspiration pneumonia, rosacea, fungating wounds, intra-abdominal infections, lung abscess, periodontitis, amoebiasis, oral infections, giardiasis, trichomoniasis, and infections caused by susceptible anaerobic organisms such as Bacteroides, Fusobacterium, Clostridium, Peptostreptococcus,Prevotella species, eradicate Helicobacter pylori along with other drugs and to prevent infection in people recovering from surgery.



Drugs of choice for the treatment of bacterial vaginosis include metronidazole and clindamycin. 



The 5-nitroimidazole drugs (metronidazole and tinidazole) are the mainstay of treatment for infection with Trichomonas vaginalis. 



With Trichomonas vaginalis both the infected patient and the patient’s sexual partner is recommended, even if asymptomatic. 



It is a treatment option for giardiasis, however, but there is an increasing incidence of nitroimidazole resistance.



In the case of Dracunculus it eases worm extraction rather than killing the worm.



Initial antibiotic therapy for less-severe Clostridium difficile colitis.



For pseudomembranous colitis treatment consists of metronidazole, vancomycin, or fidaxomicin by mouth.



Generally recommended vancomycin and fidaxomicin over metronidazole for C. difficile infection.



Vancomycin by mouth has been shown to be more effective in treating people with severe C. difficile colitis.



Entamoeba histolytica invasive amebiasis is treated with metronidazole in combination with diloxanide to prevent recurrence.



Common adverse drug reactions include: nausea, diarrhea, weight loss, abdominal pain, vomiting, headache, dizziness, and metallic taste in the mouth. 



Intravenous administration is commonly associated with thrombophlebitis. 



Infrequent adverse effects include: hypersensitivity reactions, headache, dizziness, vomiting, glossitis, stomatitis, dark urine, and paraesthesia.



Use of high doses and long-term therapy systemic are associated with the development of leukopenia, neutropenia, increased risk of peripheral neuropathy, and central nervous system toxicity.



Topical metronidazole therapy toxicities  include: local redness, dryness and skin irritation.



It is anticipated to be a human carcinogen, but the relationship between exposure to metronidazole and human cancer is unclear



It is listed as a possible carcinogen according to the World Health Organization (WHO) International Agency for Research on Cancer (IARC).



When used alone it rarely causes Stevens–Johnson syndrome, but occurs at high rates when combined with mebendazole.



Consuming alcohol while taking metronidazole may cause a disulfiram-like reaction with effects that can include nausea, vomiting, flushing of the skin, tachycardia, and shortness of breath.



It is thought to inhibit the liver metabolism of propylene glycol.



It also inhibits CYP2C9, so may interact with medications metabolized by these enzymes.



Hypothesized that it may decrease level of several cytokines, that are known to be increased in the COVID-19 infection. 



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